On February 21, Washington lobbyist Joel Johnson, ‎a seasoned Democratic activist who was a top White House adviser in President Bill Clinton's second term, emailed Podesta, saying Sanders "needs to be ground to a pulp."

He titled the email, "Friendly advice. No mercy."

"We can't start believing our own primary bulls---," Johnson wrote in the email. "This is no time to run the general. Crush him as hard as you can. Other than that, hope all is well and congrats on Nevada!"

Podesta responded, "I agree with that in principle. Where would you stick the knife in?"

Johnson, who is now the managing director with The Glover Park Group in Washington, DC, responded, "Obama betrayer (Wh will affirm). Hapless legislator (Senators/members will affirm). False promiser (policy elites will affirm). Can't win (black people will affirm)."

Messages left with both the Clinton campaign and The Glover Park Group were not immediately returned.

The exchange is one of tens of thousands of emails stolen from Podesta's Gmail account and published by WikiLeaks in recent weeks.

CNN cannot independently verify the authenticity of any of the emails but the Clinton campaign has not challenged any emails in other WikiLeaks releases.